Nuclear fuel bundle assemblies in boiling water nuclear reactors typically include a plurality of fuel rods extending in generally parallel relation one to the other from a lower tie plate. A plurality of fuel rod spacers are spaced one from another along the length of the fuel bundle assembly to maintain the lateral spacing of the fuel rods relative to one another. In addition to full-length fuel rods, fuel bundles often include part-length fuel rods which extend upwardly from the lower tie plate through a fewer number of the spacers than do the full-length fuel rods and which part-length fuel rods terminate below the upper ends of the full-length fuel rods. Additionally, one or more water rods typically upstand from the lower tie plate.
In certain fuel bundle assemblies, mechanical support for the fuel bundle is provided by a threaded connection between a pair of central water rods and the lower tie plate. Thus, the lower ends of the full-length and part-length fuel rods terminate in end plugs receivable in and axially removable from openings in the lower tie plate. Additionally, the upper ends of the full-length and part-length fuel rods have similar type end plug terminating in barbed end caps. These upper end caps facilitate removal of one or more of the fuel rods from the nuclear fuel assembly.
It will be appreciated that the fuel rods, both full-length and part-length, are not readily accessible since they are internal to the fuel bundle assemblies and do not extend up to the top of the water rod tie bar. Moreover, the full-length rods are held in place by spacers, typically about eight or nine spacers, and require a substantial force, for example, as much as 70 pounds, to axially withdraw each fuel rod from the fuel bundle assembly. The part-length rods are held by a lesser number of spacers, e.g., three spacers, and do not require as much axial force for their removal. However, the part-length rods are snapped into the lower tie plate with specially designed lower end plugs which require additional axial force for removal.
In order to withdraw a fuel rod from the fuel bundle assembly, an extractor must be able to be inserted and removed from the fuel bundle without damaging any of the assembly components including the fuel rod upper end caps, the fuel rods per se and the spacers and must pass through the assembly of fuel rods in the assembly, as well as ancillary fuel bundle structure. Further, the extractor tool must have the capacity to engage the barbed end cap of the upper end plug so that it can be used to not only withdraw the fuel rod but to reinsert a fuel rod and to reseat a partial or full-length fuel rod lower end plug into the lower tie plate. Finally, the extractor tool must be able to releasably lock onto the fuel rod's upper end plug's barbed cap so that the fuel rod can be withdrawn from the lower tie plate and the fuel assembly with the necessary pulling force, e.g., as much as 60 to 70 pounds.